Recent advances in breeding for Striga resistance in early and extra-early maturing maize for sub-Saharan Africa

A team of IITA scientists, molecular breeders, and geneticists, coordinated by the IITA early and extra-early Maize Program Lead, Baffour Badu-Apraku, recently made significant advances in the longstanding efforts of the IITA Maize Improvement Program (MIP) to develop genotypes with durable resistance to Striga parasitism using molecular markers. The major advances are: 

• Identification of genomic regions significantly associated with indicator traits for Striga resistance under infestation in early maturing tropical maize inbred lines in a genome-wide association study (GWAS) 

• Identification of quantitative trait locus (QTL) controlling resistance to Striga in two extra-early maturing maize mapping populations  
• Identification of QTL controlling resistance to Striga in an early maturing mapping population containing genes derived from a cross between normal endosperm maize and wild maize (Zea diploperennis) 

Parasitism by Striga hermonthica in sub-Saharan Africa (SSA) is a major cause of dramatic maize yield losses and threatens over 300 million people’s livelihoods. Farmers in the sub-region often experience complete crop failure under severe infestation and have been forced to abandon their farmlands.  

About two decades ago, IITA initiated a project, funded by the Rockefeller Foundation to develop high–yielding and Striga–resistant inbred lines and hybrids as well as identify QTL for marker–assisted selection (MAS) to facilitate and speed up the transfer of resistance genes into susceptible genotypes. Through this project, IITA scientists have made considerable advances in developing several maize genotypes with durable Striga resistance genes using conventional breeding approaches. They have developed several populations, varieties, inbred lines, and hybrids with durable resistance and distributed these to the national maize programs in SSA. However, progress in developing molecular markers for use in MAS has been very slow.  

Nevertheless, in 2017, with funding support from the Bill & Melinda Gates Foundation , the IITA-MIP has made remarkable progress under the DTMA/STMA Project through gene stacking in efforts to develop early and extra-early inbred lines using novel resistance genes from the wild maize that support little or no emergence of S. hermonthica into susceptible but outstanding genotypes. The scientists’ breeding efforts have resulted in developing several multiple stress–resistant early and extra-early inbred lines and hybrids with combined resistance/tolerance to Striga, drought, and low soil nitrogen.